Conduits for fluids, such as water or sewage conduits, or gas or chemical pipe, deteriorate over time. For example, many of the water mains throughout North America are made from unlined cast-iron pipe, the preferred material for water distribution systems up to the mid-1970's and beyond. Over time such pipes will deteriorate, often due to corrosion, becoming pitted and forming tubercules. This corroded material, in combination with mineral deposits, is known as encrustation and tuberculation.
Such deterioration results in leakage of the fluids, such as water or sewage, into the surrounding environment. For example, in 2013, Toronto experienced approximately 1700 water main breaks. These cause drops water pressure drops, and the leaking fluids can weaken the surrounding ground and can interfere with other underground systems, such as communication systems or other water or fluid bearing conduits. Such conduits need to be rehabilitated.
One approach to rehabilitation is to replace the deteriorated conduit. However, this can be a very costly and labour-intensive exercise; for example, if the conduit is a buried water pipe, replacement involves setting up a work area and digging up the pipe, known as “open-cut replacement”.
One solution is to deploy a cured-in-place structural liner within the conduit. For example, Canadian patent no. 2,361,960 of Mercier describes the use of a cured-in-place structural liner. The liner consists of two concentric tubular jackets (an outer and an inner jacket) made of a flexible material that are impregnated with an adhesive resin. Bonded to the inner surface of the inner jacket is a film that is impermeable to liquid to flow through the conduit. The liner is inserted into one end of a dry conduit and then pulled into place. A shaping step then occurs, where the liner is made to conform to the inner wall of the conduit. The liner is then cured in place by flowing heated water through the conduit. This causes the liner to become a rigid structure, bonded to the inner surface of the conduit.
In one example, such an approach results in a conduit lined with a polyurethane and fabric liner, typically 1/16 to ¼ of an inch thick, which is sealed in place with epoxy.
When rehabilitated conduits using a cured-in-place liner system, a goal is to create a “structural liner”—a liner that has sufficient structural and functional integrity that it will function as a replacement conduit even if the original conduit totally fails. A difficulty in using a cured-in place liner in a conduit is protrusions into the conduit, for example for service connections. When the liner is inserted, inflated and cured, a void may be created around the protrusion.
The presence of a void might leave the service able to work free, decreasing the water tightness of the seal and ultimately raising the possibility of the service becoming detached from the structural liner. The cured-in-place liner is supposed to last for decades in constant use.
Clients are increasingly insisting upon quality metrics for conduits after they have been rehabilitated by a cured in pipe system.